1. Field of the Invention
This invention relates to a reference table tilting mechanism for setting a reference table to have a desired angle of inclination, and in particular to a reference table tilting mechanism which is designed to have a simplified structure and a high rigidity, and to manufacture at a low cost.
2. Related Art Description
The conventional manual operating reference table tilting mechanism has a reference table whose inclination angles of x and y directions are adjusted manually with using a track level. While, there has also been known an automatic reference table tilting mechanism which is typically constituted to have an inclination detecting sensor (one-dimensional or two-dimensional sensor) mounted on a reference table, a servo controller and a servo actuator for tilting the reference table. The servo controller is provided with an output of the sensor and an input signal representing a desired angle, and, based on the difference between the two parameters, controls the servo actuator. A linear type actuator is used as the servo actuator.
An object of this invention is to provide a reference table tilting mechanism which is constituted to have a single reference table, so that it has a simplified structure and a high rigidity, and can be manufactured at a low price in comparison with the conventional reference table tilting mechanisms.
Further, an object of this invention is to provide a reference tilting mechanism which employs an eccentric cam type mechanism as a servo actuator for adjusting an angle of inclination of a reference table instead of a linear type actuator, whereby a driving portion thereof can be made to have a high torque amplification and can be manufactured at a low price.
In order to solve the above and other objects, a reference table tilting mechanism according to this invention comprises a reference table, first and second eccentric cam type angle adjusting means for adjusting an angle of inclination of the reference table, and a spring means for supporting the reference table.
The first eccentric cam type angle adjusting means has an eccentrically rotatable first disc shaped cam, a contact point of which with the reference table is designed to move vertically with respect to the reference table as the first disc shaped cam is rotated eccentrically. Likewise, the second eccentric cam type angle adjusting means has an eccentrically rotatable second disc shaped cam, a contact point of which with the reference table is located different from that of the first disc shaped cam and moves vertically with respect to the reference table as the second disc shaped cam is eccentrically rotated.
The spring means supports the reference table at a point which is located different from each of the contact points of the first and second disc shaped cams.
In a preferred embodiment, the spring means presses the reference table against the first and second disc shaped cams with a predetermined resilient force. With this constitution, since the first and second eccentric cam type angle adjusting means are applied with a pre-load, backlash thereof can be eliminated to realize a high accurate tilting adjustment.
Typically, the reference table tilting mechanism comprises a first angle sensor for detecting an angle of inclination in a first direction of the reference table, and a second angle sensor for detecting an angle of inclination thereof in a second direction of the reference table, the first and second directions being different from each other. Further, it has a control means for controlling to drive the first and second eccentric cam type angle adjusting means in accordance with detected angles by the first and second angle sensors so that the reference table is adjusted to have a desired angle of inclination.